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(11) | EP 1 074 346 A2 |
| (12) | EUROPEAN PATENT APPLICATION |
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| (54) | Toothed abrasive wheel |
| (57) A toothed abrasive wheel (4) is designed for increasing the degree of aggressiveness
on the surface to be worked and the degree of cooling and chip evacuation, and has
an annular active band (TP) with patterns of teeth (5) arranged in series along broken
or continuous spiral arcs which are concave in an inward direction in the two possible
directions of rotation, with a tangential component; each series of teeth (5) having
an irregular rhomboidal base is flanked by a pair of channels (6) which separates
it from the contiguous series; air and chip evacuation occurs along the channels (6);
the wheel is used in industrial coarse grinding and lapping of surfaces, particularly
as a manual tool driven by an electric motor. |
[0001] The invention relates to a toothed abrasive wheel, i.e. to a disk-like abrasive tool provided with raised portions on its active annular band for working surfaces, for example metallic ones, for coarse grinding or lapping.
[0002] The prior art comprises an abrasive wheel with closely spaced frustum-shaped teeth arranged along radial directions on concentric circles of the active band; said circles are mutually spaced, from the center towards the rim, by an extent which is less than the sum of the base radii of said teeth: this produces a pattern of teeth on alternately staggered radial half-lines in which the tooth size increases towards the rim (height being equal). However, such a frustum-like shape and such a distribution of teeth close to each other and staggered in this manner forms passages along winding paths across said active band from the center towards the rim which do not facilitate, and indeed hinder, due to their path and direction, evacuation of the air and of the chip during work, leading to overheating and clogging problems. Moreover, the frustum-like shape of said teeth does not have adequate characteristics of aggressiveness of the abrasive of the wheel with respect to the surface to be worked, because the only cutting element is constituted, in the frustum-shaped mass of the tooth, by the circular edge of the smaller base of the frustum.
[0003] This prior art is susceptible of considerable improvements as regards the possibility to avoid, or in any case reduce, the above-noted drawbacks.
[0004] The above leads to the necessity to innovate, finding a tooth shape and a tooth distribution in the active band of the disk-like abrasive wheel which allow: a better degree of aggressiveness of the abrasive on the surface to be worked, more efficient and unhindered channeling of the air from the center to the rim in both directions of rotation, in order to achieve more effective cooling of the abrasive wheel and more effective chip evacuation, so as to avoid clogging with consequent attenuation of the degree of aggressiveness.
[0005] The invention achieves the intended aim by adopting a tooth which is shaped like a truncated prism, since it has longer edges, in order to improve the degree of aggressiveness of the active band of the abrasive; the distribution of such a shape of the teeth having to allow channeling of the air and of the chip from the center towards the rim, in both directions of rotation of the abrasive wheel, by way of channels whose path, constituted by a succession of straight or arc-like segments which constitute the base side of the truncated prism, is substantially concave in an inward direction and has a component which is tangential at least at the rim of the abrasive wheel in both directions of rotation: said segments mutually intersecting so as to form a grid of prism-shaped teeth which are uniformly distributed and increase in size from the center towards the rim and are as high as the active layer of the abrasive wheel is deep; advantageously, the type of the prism being a pyramid with an irregular rhomboid base.
[0006] The advantages achieved by the present invention are: provision of a number of tool edges equal to the number of edges of the prisms included in the annular active band, and therefore higher aggressiveness; provision of a pattern of paths which are substantially arc-like and shaped like a spiral segment, in both directions of rotation, in order to channel the air and the chip towards the rim, and therefore higher cooling capacity of the abrasive wheel and lower likelihood of clogging.
[0007] An embodiment of the toothed abrasive wheel according to the invention is shown as an example in the accompanying four drawing sheets, wherein:
Figure 1 is a front view of the conventional toothed abrasive wheel, with frustum-shaped teeth distributed over the active band along radial half-lines and along circles which are concentric with respect to the center of the abrasive wheel and have diameters increasing by an extent which is less than the sum of the gradually increasing base diameters of the successive frustum-shaped teeth, in order to achieve the highest possible tooth density;
Figure 2 is an enlarged-scale view of a detail of a sector of the active band of the conventional abrasive wheel of Figure 1, illustrating the winding path, from the center towards the rim, of the narrow gaps between the teeth, which do not facilitate, but do even hinder, the formation of a path for the peripheral escape of air and of the resultant chip;
Figure 3 is instead a front view of the abrasive wheel according to the invention, toothed with truncated prism-like shapes which in the example are truncated pyramids having an irregular rhomboid base;
Figures 4 and 5 are sectional views, taken along the central planes designated by IV-IV, V-V, in the case of a flat abrasive wheel and of a convex abrasive wheel, respectively;
Figure 6 is a plan view of a diagram of the tracing of the base grid of the toothed surface of Figures 3, 4 and 5, obtained by means of straight or curved segments, according to the angular spacing of the radial half-lines, with preset inclinations with respect to each one of said half-lines;
Figure 7 is a plan view of the appearance of the toothed surface of Figure 6, advantageously provided with teeth which are shaped like truncated pyramids with an irregular rhomboid base, as obtained from the diagram of Figure 6;
Figure 8 is a sectional view, taken along the plane VIII-VIII, shown for the sake of clarity in Figure 6 but related to the corresponding and more complete Figure 7, illustrating the profile of the truncated-pyramid teeth with respect to the bottom of the channel;
Figures 9 and 10 are, likewise, sectional views, taken along the planes IX-IX and X-X of Figures 6 and 7, passing through the centerline of the teeth, respectively in the case of a flat abrasive wheel and of a convex abrasive wheel.
[0008] TC designates the active band of the disk-like abrasive wheel 1, which is provided with conventional frustum-shaped teeth 2; 3 designates winding channels which separate the teeth 2, proceeding from the center towards the rim; TP (see Figure 3) designates the active band of a disk-like abrasive wheel 4 provided with teeth shaped like a truncated prism (in this case, advantageously, shaped like a truncated pyramid with irregular rhomboid base); r designates the radial half-lines that originate from the center of the abrasive wheel and lie on the base plane of its active surface; ⌀i, ⌀e (in fact, in Figure 6 the radii Ri and Re are represented which obviously are equal to ⌀i/2 and ⌀e/2) respectively designate the inside diameter and the outside diameter of the active band TP; A designates the angle of the sector that lies between the contiguous half-lines r, constituting the angular spacing of the teeth according to the invention; f designates the straight or curved segment constituting the broken line element that forms the substantially curved path (in the example, similar to a spiral segment) of the bottom of the channel 6 that separates the teeth; this element is orientated obliquely to the two radial half-lines r that intersect each segment thereof, both in the clockwise direction and in the counterclockwise direction, and thus is provided with a peripheral tangential component; P designates the angle formed by each portion f of path with the radial half-line r that passes through the initial end of said segment, for each one of the two oblique directions; c designates the maximum width of the channel 6, which is reached on the top plane of the teeth 5; S (see Figures 8, 9, 10) designates the depth of the active band TP, i.e. the depth of the channels 6.
[0009] It is noted that ⌀i, ⌀e (respectively Ri and Re) can assume any value necessary to meet operating requirements.
[0010] As regards the angle A, it can assume values at the most within a range (2° to 30°), like the angle P (10° to 60°).
[0011] As regards the angle P formed by the successive segments f along a same path, its value can vary by a few degrees along said path.
[0012] The following ranges of angular values for the following ranges of outside diameters are preferable and advantageous:
for ⌀e between 115 and 125 mm
A: 11° to 13°, particularly 11.5°
P: 45° to 55°, particularly 50°
for ⌀e between 175 and 185 mm
A 9° to 11°, particularly 10°
P 55° to 65°, particularly 60°
[0013] In practical execution, the materials, the dimensions, the constructive details, the angular distance A between the half-lines r, the value of the angle P, the depth s may be different from the ones given, but technically equivalent thereto, without thereby abandoning the concept of the appended claims.
[0014] Moreover, the profile of the transverse cross-section of the channels 6 between each pair of teeth 5 can be two-sided (V-shaped, as in the illustrated example) or three-sided or arc-like, with a maximum width, at the top of the teeth, on the order of a few millimeters.
[0015] As regards the construction of the grid of paths, it can be obtained graphically, with or without calculations, on the basis of the above indicated values, taking into account contingent requirements.
[0016] The disclosures in Italian Utility Model No. MO99U000039 from which this application claims priority are incorporated herein by reference.
[0017] Where technical features mentioned in any claim are followed by reference signs, those reference signs have been included for the sole purpose of increasing the intelligibility of the claims and accordingly such reference signs do not have any limiting effect on the scope of each element identified by way of example by such reference signs.
for ⌀e between 115 and 125 mm
A: from 11° to 13°, advantageously 11.25°;
for ⌀e between 175 and 185 mm
A: from 9° to 11°, advantageously 10°.
for ⌀e between 115 and 125 mm
P: from 45° to 55°, advantageously around 50°, with variation of a few degrees or fractions of a degree for the successive segments of the broken line in a same path;
for ⌀e between 175 and 185 mm
P: from 55° to 65°, advantageously around 60°, with variation of a few degrees or fractions of a degree for the successive segments of the broken line in a same path.